1. Field
This invention pertains to a safety valve useful in well conduits which is actuated to close by production flow impingement on a flow choke in the valve. These safety valves are also known as pressure differential operated or direct acting safety valves.
2. Related Art
A number of U.S. Patents have issued for direct acting safety valves which utilize poppet, ball or flapper valves and include ball type detent mechanisms to hold the valve open until an actuating flow rate through the choke is reached and then permit very quick or "snap" closure of the valve.
An example of a safety valve actuated by flow with ball type snap closure feature utilizing a poppet type valve is shown in U.S. Pat. No. 3,070,119 to Raulins entitled WELL TOOLS. This valve utilizes a "bean" or flow choke which cannot be retrieved from the valve and resilient material `o` rings for seals.
U.S. Pat. No. 3,126,908 to Dickens for WELL TOOLS discloses a pressure operated valve with ball type snap closure structure which employs a ball type main valve. The valve also has a bean which cannot be retrieved and uses a number of resilient material `o` rings for sealing.
Another U.S. Pat. No. 4,664,195 for SAFETY VALVE to Deaton shows a direct acting safety valve having a main flapper type valve and using resilient material seal means. Resilient seals rapidly deteriorate and leak in the high temperature and corrosive environment found in deeper wells.
U.S. Pat. No. 4,362,214 to Pringle and Morris disclose a flapper type differential actuated well safety valve having a housing, a valve element, a flow tube, spring means, a choke bean and releasable connecting means for connecting the choke bean to and releasing it from the flow tube by longitudinal movement of the bean relative to the flow tube.